Hello there,
Well, of course you are very very bad, and no-one else has ever missed a booster !!!

You wrote that the ewes were born March 2016.... if so, then they should have had two lots of injections in or around May and June, so their booster would not be due until summer of this year....
If they've never had a set of vaccinations then obv you want to start asap with the two shots, four weeks apart. If they've missed an annual booster, then personally I would start the two shots again now...
With our ewe lambs, once they actually start lambing themselves it seems to me that one year they will get their booster earlier than usual, since they will have gone from annual 'lamb' shots in May/June to annual 'in lamb' shots around February / March...(does that make sense?)...
(btw, our vets have said the annual booster for cats (don't know about dogs) actually would last about 15 months... so who knows, maybe the same with ovines!)
As for the cough - could be something or nothing.... ours will have a good cough every now and then...I'm only concerned if the same one has one repeatedly over a couple of days...
Coughing can be a symptom of lung worm - and is treated with most usual wormers ...
If it were my sheep and I became v worried but couldn't get hold of the vet then I'd give a shot of ab just in case there's a respiratory infection brewing...
good luck!
